1. Field of the Invention
This invention relates to an initial state-setting circuit and, more particularly, to a circuit for setting the state of a memory circuit, such as a flip-flop circuit, to a predetermined state after closure of a power supply switch.
2. Description of the Prior Art
In digital equipment, such as electronic desk top calculators and digital measuring instruments, numerous memory circuits are employed. In using such equipment, it is necessary to set the contents of the memory circuit, e.g. a register, to predetermined contents or clear the memory circuit after closure of a power supply switch. The applicants of the present application have proposed circuits for automatically effecting the clear operation in the specifications of (Japanese) Patent Application No. 61980/1973, Patent Application No. 61982/1973 and Patent Application No. 78368/1973.
The automatic clear circuit employs a flip-flop circuit in which the charging time constant of the gate capacitor of one transistor is different from that of the gate capacitor of the other transistor, or in which the output potentials of respective inverter circuits during steady state are different from each other. That is, it employs an asymmetric flip-flop circuit. Since the flip-flop circuit is asymmetric, the initial state after the closure of the power supply switch can be normally set at a stable point on one side.
The automatic clear circuit, however, is not always perfect, and can cause a malfunction due to noise of from an input source of the flip-flop in some operations.